自组装GaN量子点结构的ECR－PAMOCVD生长及特性

The quantum dots (QDs) structure materials with three dimensions quantum confinement effect have unique physics properties, which are not only significance for semiconductor physics and material science, but also foundation of new generation of electronic and photo-electronic devices. Comparing with quantum well lasers, the QDs lasers have lower threshold current densities, higher differential gain, and better temperature characteristics. By using the strain self-organization technique based on Stranki Krastanov (SK) growth mode, the QDs structure and QDs lasers with wavelength range covering red and infrared range have been developed, and the CW wave emission from base state QDs laser has been obtained. Although III-V nitrides are vary attractive region due to their promising application of photo-electronic device for short wavelength range, there still have some basic problems to probe, for example the strain relaxation of hetero-structure with large lattice mismatch. Especially, the quantum scale effect of III group nitrides QDs structure are interested very much. Based on the work of last NSFC, this subject investigate the growth and characteristics of strain self-organization GaN/AlN QDs structure by the electron cyclotron resonance (ECR) microwave plasma enhanced MOCVD (PEMOCVD) controllable low-temperature epitaxy technique. For this purpose, the ECR-PEMOCVD system (ESPD-U) equiped with reflection high-energy electron diffraction (RHEED) has been developed for the first time; the dependence of qualities of GaN and AlN films on the crystal quality and surface morphology of GaAs and sapphire substrates, the plasma pretreatment of the substrates, buffer layer growth, the V/III ratio and the temperature were investigated by RHEED monitoring in situ, and the ECR-PEMOCVD epitaxy technology was improved; furthermore, growth and characteristics of the large lattice mismatch hetero-junction, GaN/Al2O3(0001), c-GaN/GaAs(001) AlN/Al2O3(0001), and AlN/GaN/ Al2O3(0001) were investigated; The strain relaxation in epitaxial growth of lattice mismatch hetero-junction of III group nitrides was investigated by RHEED monitoring in situ. It was found by RHEED observing in situ that the 30°rotations of the (0 0 0 1) nitride plane and (0001)AlN epilayer with respect to (0001) planes of the sapphire substrate and GaN buffer layer occur respectively to reduce the lattice constant mismatch, which is very important for the research of formation mechanism of dislocation and growth mode. Based on these investigations, GaN/AlN QDs structures were grow by ECR-PEMOCVD. The density of the QDs is 1010 cm-2 , and the diameter and high are about 30-40nm and <15nm respectively. The density and size of the QDs dependant on growth temperature andⅤ/Ⅲ ratio, and crystalline quality and surface smoothness of AlN film. The GaN QDs on GaAs(001) substrate were prepared by strain energy release induced by high temperature annealing. The density of GaN QDs is 1010-1011 cm-2 and the diameter is 30nm and high about 14nm. The density and size of GaN QDs dependant on the temperature and the duration of depositing and annealing. The nucleation mechanism of GaN QDs is discussed. Based on equilibrium reaction thermodynamic theory, low-temperature epitaxial growth of GaN film are analyzed. A chemical equilibrium model was given. Through calculation we got the key factors and phase diagram of hexagonal GaN growth and firstly got the key factors and phase diagram of cubic GaN growth. The results of theoretical calculation are consistent with our experimental results.

量子点结构材料独特的物理性质不仅对半导体物理本身极其重要，而且是下一代量子器件的基础。自组装量子点的制备、特性及应用研究是目前国际上的前沿课题。本项目拟采用我们首次提出的ＥＣＲ－ＰＡＭＯＣＶＤ可控活化低温外延技术，借助于成功的等离子体处理工艺，研究在ＡｌＮ上自组装ＧａＮ量子点的制备；研究控制量子点尺寸密度分布的均匀性及光发射特性。